The present invention relates to the crosslinking and simultaneous alkylation of poly(hydridomethylsiloxanes) to form crosslinked siloxanes having n-alkylmethyl groups. Without changing the chain length of the poly(hydridomethylsiloxane) starting material, a family of lightly crosslinked siloxanes having n-alkylmethyl groups can be produced using one or more alpha-olefins along with a small amount of an unconjugated alpha, omega-diene added as a crosslinker. The lightly crosslinked siloxanes having n-alkylmethyl groups have a wide range of viscosities. The poly(hydridomethylsiloxanes) are made from highly pure silanol-free hexamethyldisiloxane and highly pure mixtures of silanol-free tetramethylcyclotetrasiloxane (D.sup.H 4) and pentamethylcyclopentasiloxane (D.sup.H 5) containing no more than about 100 parts per million (ppm) water, with anhydrous trifluoromethane sulfonic acid (triflic acid, CF.sub.3 SO.sub.3 H), at room temperature, to provide linear poly(hydridomethylsiloxanes) (MD.sup.H.sub.x M) where x is from 8 to 250. These crude polymers are neutralized by solid NaHCO.sub.3 and filtered to remove Na+ triflate to provide the neutral poly(hydridomethylsiloxanes).
To the poly(hydridomethylsiloxanes) are added a reaction mixture consisting of a catalyst, alpha-olefin and a crosslinker which is an unconjugated alpha, omega-diene. The resulting lightly crosslinked siloxanes having n-alkylmethyl groups are waxes or fluids at room temperatures, and can be used in a variety of applications where controlling viscosity of the polymer is critical. The compositions of the present inventions are especially useful as an additive to toner used in photocopiers.
The present invention utilizes these new ultra pure polymers to make a dramatic advance in the art. Heretofore, the available siloxanes having n-alkylmethyl groups were not predominately linear like those used as starting materials herein, but contained significant branch sites. When crosslinker was added to the branched polymers the resulting compositions had extremely high viscosities, sometimes forming useless gels. Moreover, adding even incremental amounts of crosslinker to otherwise useful compositions would result in excessively high viscosity materials; this creates major production difficulties where minor variations in the amount of crosslinker could result in lots varying widely in viscosity or rendered otherwise unusable. The non-branched starting materials of the present invention eliminated this problem. Furthermore, the previously available siloxanes were typically contaminated with highly reactive residual SiH, resulting in unstable compositions whose viscosities increased over time. The crosslinked siloxanes of the present invention do not include detectable amounts of residual SiH and are therefore stable over time.
Our invention, therefore, is in sharp contrast to the gel containing crosslinked oily materials taught in U.S. Pat. No. 2,491,843 (Dec. 20, 1949); or the crosslinked high polymers bearing SiOH end groups, described in the European Polymer Journal, Vol. 29, No. 1, Pages 15-22, (1993). Furthermore, our alkylated products are prepared from highly pure essentially anhydrous silanol-free starting materials and contain low or no residual silicon hydride functionality.